GPT-4.5 vs GPT-5.1 Codex
Side-by-side benchmark comparison across coding, math, reasoning, speed, and pricing.
GPT-5.1 Codex by OpenAI wins on 13 of 14 benchmarks against GPT-4.5 by OpenAI, which leads on 1. This head-to-head comparison covers coding, math, reasoning, speed, and pricing metrics from our benchmark data.
Category-by-Category Breakdown
General Intelligence: In general intelligence, GPT-5.1 Codex scores 1395 on Chatbot Arena ELO compared to GPT-4.5's 1310, while GPT-5.1 Codex scores 82.0% on MMLU-Pro compared to GPT-4.5's 78.0%.
Coding: In coding, GPT-5.1 Codex scores 96.0% on HumanEval+ compared to GPT-4.5's 88.0%, while GPT-5.1 Codex scores 78.0% on SWE-bench Verified compared to GPT-4.5's 38.0%, while GPT-5.1 Codex scores 85.0% on LiveCodeBench compared to GPT-4.5's 45.0%.
Math: In math, GPT-5.1 Codex scores 85.0% on MATH compared to GPT-4.5's 82.0%, while GPT-5.1 Codex scores 95.0% on GSM8K compared to GPT-4.5's 94.0%.
Reasoning: In reasoning, GPT-4.5 scores 71.4% on GPQA Diamond compared to GPT-5.1 Codex's 65.0%, while GPT-5.1 Codex scores 52.0% on ARC-AGI compared to GPT-4.5's 20.0%.
Context: In context, GPT-5.1 Codex scores 400K on Context Length compared to GPT-4.5's 128K.
Pricing Comparison
GPT-4.5 costs $75.0/1M input tokens and $150.0/1M output tokens, while GPT-5.1 Codex costs $1.3/1M input and $10.0/1M output. GPT-5.1 Codex is the more affordable option for API usage.
Speed Comparison
GPT-4.5 generates output at 60 tok/s compared to GPT-5.1 Codex's 85 tok/s, and the time to first token is 600 ms for GPT-4.5 versus 400 ms for GPT-5.1 Codex. GPT-5.1 Codex delivers faster throughput.
Verdict
GPT-5.1 Codex leads across the board in coding, general intelligence, math, affordability, speed, making it the stronger overall choice in this comparison.
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GPT-4.5 vs GPT-5.1 Codex — FAQ
Which is better, GPT-4.5 or GPT-5.1 Codex?
GPT-5.1 Codex wins on more benchmarks overall (13 vs 1). However, the best choice depends on your specific needs — each model excels in different areas.
How does GPT-4.5 compare to GPT-5.1 Codex for coding?
GPT-5.1 Codex is better for coding, scoring 78.0% on SWE-bench Verified compared to 38.0%. SWE-bench tests real-world software engineering by resolving actual GitHub issues.
Is GPT-4.5 cheaper than GPT-5.1 Codex?
Yes, GPT-5.1 Codex is cheaper. GPT-4.5 costs $75.0/1M input and $150.0/1M output tokens. GPT-5.1 Codex costs $1.3/1M input and $10.0/1M output tokens.
Which is faster, GPT-4.5 or GPT-5.1 Codex?
GPT-5.1 Codex is faster, generating output at 85 tok/s compared to 60 tok/s. Faster output speed means shorter wait times for API responses.
What benchmarks does the GPT-4.5 vs GPT-5.1 Codex comparison cover?
This comparison covers 14 benchmarks including Chatbot Arena ELO, MMLU-Pro, HumanEval+, MATH, GPQA Diamond, SWE-bench Verified, Output Speed, LiveCodeBench, and more. Metrics span general intelligence, coding, math, reasoning, speed, and cost categories.